Communication system for telephone line access with crosstalk mitigation

ABSTRACT

The present disclosure includes systems and techniques relating to wired communication channels, such as telephone lines in a bundled telephone cable. In some implementations, a system includes telephone lines bundled together; electronic equipment including a first transceiver device for each of the telephone lines, which is configured to coordinate transmissions over a respective telephone line; and second transceiver devices coupled respectively with the telephone lines such that each second transceiver device is respectively paired with a first transceiver device; each pair of first and second transceiver devices is configured to communicate over the respective telephone line connecting the pair using a Medium Access Control (MAC) cycle split into predefined time slots for downstream communication and upstream communication; and the first transceiver devices are synchronized with each other to align the MAC cycle and the predefined time slots across the telephone lines.

CROSS REFERENCE TO RELATED APPLICATIONS

This disclosure claims the benefit of the priority of U.S. ProvisionalApplication Ser. No. 61/932,585, filed Jan. 28, 2014 and entitled “NEXTMITIGATION TECHNIQUE FOR G.HN TECHNOLOGY USED FOR DSL-LIKE PHONE LINEACCESS APPLICATIONS”, which is hereby incorporated by reference in itsentirety. In addition, this disclosure is related to U.S. ProvisionalApplication Ser. No. 61/932,599, filed Jan. 28, 2014 and entitled“MODIFICATIONS TO THE G.HN STANDARD FOR DSL-LIKE PHONE LINE ACCESSAPPLICATIONS: FEXT STABILITY”, which is hereby incorporated by referencein its entirety.

BACKGROUND

The present disclosure describes systems and techniques relating towired communication channels, such as telephone lines in a bundledtelephone cable.

G.hn is a home networking standard developed by ITU (InternationalTelecommunications Union). The G.hn standard describes a multi-nodenetwork (similar to a WiFi network) that shares a channel (power line,phone line or coax cable). A network is known as a “domain” in thestandard. A domain is controlled by a single node called Domain Master(DM). The Domain Master is in charge of coordinating the transmissionsof all the nodes in the network (scheduling) to avoid collisions in thechannel and guarantee a required level of quality of service (QoS) tothe traffic conveyed in the domain. Each node can communicate with anyof the other nodes of the domain (multi-point to multi-pointcommunications).

On the other hand, the architecture of DSL (Digital Subscriber Line)phone line access applications is different. The architecture of DSL isbased on a pair of nodes that communicate with each other: one node isplaced at the customer side, referred to as the CPE (Customer PremisesEquipment), and the other node is an operator node placed at thetelephone company side, typically along with other operator nodes in aDSLAM (DSL Access Multiplexer). Since several operator nodes aretypically collocated at the DSLAM, the operator odes have the potentialto interfere with each other, as phone lines run together from the DSLAMto each of the customer premises and can suffer from crosstalk among thephone lines. There are two sources of interference: NEXT (near endcrosstalk) interference from one operator node to another operator node,and FEXT (far end crosstalk) interference from one operator node to theCPEs of other lines (or the other way around; interference from one CPEto the operator nodes of other lines). DSL standards have developeddifferent ways of overcoming this interference. In addition,improvements have been proposed for DSL to increase its speed; suchproposals are often referred to as VDSL.

SUMMARY

The present disclosure includes systems and techniques relating to wiredcommunication channels, such as telephone lines in a bundled telephonecable. G.hn technology is being observed as an alternative to a nextgeneration of VDSL. However, the network architecture of G.hn has beendesigned for use as a home network connecting several devices using anyof the available cables in a home (over AC (Alternating Current) powerlines, telephone lines or coaxial lines). As described herein, G.hntechnology can be modified improve utility in a DSL-like communicationsystem.

According to an aspect of the described systems and techniques, a systemincludes telephone lines that cover a distance from a first location toseparate points at second locations, where the telephone lines arebundled together in a same telephone cable for at least a portion of thedistance; electronic equipment located at the first location, theelectronic equipment including a first transceiver device thr each ofthe telephone lines, where each first transceiver device at the firstlocation is configured to coordinate transmissions over a respectivetelephone line coupled with the first transceiver device; and secondtransceiver devices coupled respectively with the telephone lines at thesecond locations, such that each second transceiver device isrespectively paired with a first transceiver device at the firstlocation; where each pair of first and second transceiver devices isconfigured to communicate over the respective telephone line connectingthe pair using a Medium Access Control (MAC) cycle that is split intopredefined slots in time for (i) downstream communication from the firsttransceiver device to the second transceiver device and (ii) upstreamcommunication from the second transceiver device to the firsttransceiver device; and where the first transceiver devices aresynchronized with each other to align the MAC cycle and the predefinedtime slots across the telephone lines.

Each transceiver device at the first location can be configured tooperate in accordance with a specification designed for multi-point tomulti-point communications over home electrical wiring, at least one ofthe second locations can have more than one second transceiver devicecoupled with a single telephone line, and the more than one secondtransceiver device can share the upstream communication slots on thesingle telephone line. The specification can be a G.hn specification. Inaddition, a Zero Cross signal input of each of the first transceiverdevices can be connected to a common reference clock to synchronize thefirst transceiver devices.

The predefined slots in time can have an unbalanced distribution betweendownstream communication and upstream communication. The unbalanceddistribution can assign more time slots to downstream communication thanupstream communication, and time slots assigned to upstreamcommunication can be distributed to reduce latency. In some cases, theunbalanced distribution can assign seven of each ten slots to downstreamcommunication and three of each ten slots to upstream communication.Moreover, each one of the first transceiver devices can be configured touse a preamble that is different from each other preamble used byremaining ones of the first transceiver devices, and the firsttransceiver devices can be configured to use up to three hundreddifferent preambles.

According to an aspect of the described systems and techniques, atransceiver device includes a coupling circuitry configured to connectwith a telephone line that is bundled with additional telephone lines ina telephone cable; an analog front end coupled with the couplingcircuitry; and a controller coupled with the analog front end andconfigured to coordinate transmissions over the telephone line; wherethe controller is configured to split a Medium Access Control (MAC)cycle for the transmission into predefined slots in time for (i)downstream communication to another transceiver device coupled with thetelephone line and (ii) upstream communication from the othertransceiver device; and where the controller is configured tosynchronize the MAC cycle with MAC cycles of additional transceiverdevices coupled with the additional telephone lines in the telephonecable to align all the MAC cycles and the predefined time slots acrossthe telephone lines.

The coupling circuitry, the analog front end, and the controller can beconfigured to operate in accordance with a specification designed formulti-point to multi-point communications over home electrical wiring.The specification can be a G.hn specification. The transceiver devicecan include a Zero Cross signal input connected to a common referencedock to synchronize all the MAC cycles and the predefined time slotsacross the telephone lines.

The controller can include a baseband digital signal processorprogrammed to use an unbalanced distribution for the predefined timeslots between downstream communication and upstream communication. Thebaseband digital signal processor can be programmed to assign more timeslots to downstream communication than upstream communication and todistribute time slots assigned to upstream communication to reducelatency. The baseband digital signal processor can be programmed toassign seven of each ten slots to downstream communication and three ofeach ten slots to upstream communication.

The controller can be configured to use a preamble that is differentfrom each of other preambles used by the additional transceiver devices.The controller can be configured to select the preamble from a set ofthree hundred different available preambles.

According to an aspect of the described systems and techniques, a methodincludes selecting an orthogonal preamble from a set of availablepreambles for use on a telephone line that is bundled with additionaltelephone lines in a telephone cable; synchronizing a Medium AccessControl (MAC) cycle with MAC cycles of additional transceiver devicesconnected respectively to the additional telephone lines bundled in thetelephone cable; splitting the MAC cycle into predefined time slotsaligned across communications on the additional telephone lines by theadditional transceiver devices, where the predefined time slots includetime slots for downstream communication and time slots for upstreamcommunication; sending communication signals on the telephone line inthe downstream time slots using the selected orthogonal preamble; andreceiving communication signals on the telephone line in the upstreamtime slots.

The selecting can include selecting the orthogonal preamble from a setof three hundred different available preambles. The method can includeusing an unbalanced distribution for the predefined time slots betweendownstream communication and upstream communication. The can include:assigning more time slots to downstream communication than upstreamcommunication; and distributing time slots assigned to upstreamcommunication to reduce latency. In addition, the assigning can includeassigning seven of each ten slots to downstream communication and threeof each ten slots to upstream communication.

The described systems and techniques can be implemented in electroniccircuitry, computer hardware, firmware, software, or in combinations ofthem, such as the structural means disclosed in this specification andstructural equivalents thereof. This can include at least onecomputer-readable medium embodying a program operable to cause one ormore data processing apparatus (e.g., a signal processing deviceincluding a programmable processor) to perform method operations. Thus,program implementations can be realized from a disclosed method, system,or apparatus, and apparatus implementations can be realized from adisclosed system, computer-readable medium, or method. Similarly, methodimplementations can be realized from a disclosed system,computer-readable medium, or apparatus, and system implementations canbe realized from a disclosed method, computer-readable medium, orapparatus.

The described systems and techniques can result in a communicationsystem for telephone line access that uses transceivers in a manner thatreduces interference. For example, rather than having G.hn domainsworking independently of each other, G.hn domains on separate telephonelines that share a bundled telephone cable can work synchronously witheach other, all transmitting or receiving at the same time. Thus, highlevels of interference caused by one DM transmitting while another DM ona close line is receiving can be substantially reduced, if noteliminated, and the maximum achievable performance can be improved.Synchronizing transmission and reception across multiple lines reducesthe interference caused by random relative timings of communications,thus easing the process of channel adaptation and reducing bit errorrates. In addition, network setup can be made less difficult.

Interference produced in reception by near equipment that istransmitting can be avoided. This enables an increase in communicationperformance and stability. Accurate synchronization can allow timedivision into short slots, which can reduce latencies and enable theconfiguration of percentages for upstream and downstream directions. Inaddition, proper connection of each CPE to its corresponding (installedon the same phone pair) can be better ensured, and disturbance ofservice of near G.hn domains can be reduced. Isolation among differentpairs can increase performance and reduce network setup. Moreover, thenoted improvements can be advantageous in combination with systems andtechniques used to provide FEXT stability, as described in U.S.Provisional Application Ser. No. 61/932,599, filed Jan. 28, 2013, andalso described in detail below.

Details of one or more implementations are set forth in the accompanyingdrawings and the description below. Other features and advantages may beapparent from the description and drawings, and from the claims.

DRAWING DESCRIPTIONS

FIGS. 1A and 1B respectively show a bundled telephone cable and acommunication system that uses the bundled telephone cable.

FIG. 2A shows an example of a transceiver device.

FIG. 2B shows an example of a communication system with transceiverdevices synchronized for communication on separate wires that share acommon cable.

FIG. 2C shows an example of an unbalanced distribution betweendownstream communication and upstream communication for predefined timeslots in the communication system of FIG. 2B.

FIG. 3 shows an example of a process for communicating on a phone lineof a bundled telephone cable having multiple phone lines.

FIG. 4 shows an example of a process for increasing stability of signalto noise ratio estimation on a phone line of a bundled telephone cablehaving multiple phone lines.

FIG. 5 shows an example of a communication system with differentconcurrent operations of transceiver devices coupled with separate wiresthat share a common cable.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1A shows a bundled telephone cable 100, which is a common type oftelephone cable used the existing installed infrastructure of telephonesystems. The bundled telephone cable 100 includes multiple separatetelephone lines 110 that are grouped together in the telephone cable100, where the phone lines 110 go from a central location, such as alocal carrier end office, to separate customer premises. Each phone line110 can be a twisted pair of wires, or a twisted and not twisted pair ofwires, with each wire having a solid copper conductor 112 and an outerinsulator 114.

Bundled telephone cables 100 can include many phone lines 110, such asseventy five, one hundred, one hundred and fifty, or three hundred pairsof copper wires 110. In other cases, there are fewer pairs of wires(e.g., 10, 20, 25, etc.). Each twisted copper wire pair can be wrappedin shielding before being grouped with other wire pairs in a jacket.Nonetheless, signals on one wire pair can induce interference on anotherwire pair in the bundled telephone cable due to the close proximity ofthe wires. Such interference includes NEXT interference, where a signalbeing transmitted from a first end of the bundled telephone cable on onewire pair interferes with the signals being received at that same firstend on another wire pair in the bundled telephone cable. Suchinterference also includes FEXT interference, where a signal beingtransmitted from a first end of the bundled telephone cable on one wirepair interferes with the signals being received at a second end of thebundled telephone cable on another wire pair in the bundled telephonecable.

FIG. 1B shows a communication system that uses the bundled telephonecable 100 from FIG. 1A. The bundled telephone cable 100 includesmultiple phone lines 110 connecting electronic equipment 120 at a firstlocation (e.g., a central office 125 or a local carrier end office) toseparate transceiver devices 130 at separate customer premises a house135). The electronic equipment 120 includes multiple transceiverdevices, one for each of the separate transceiver devices 130 at theother end of the phone lines 110. The electronic equipment 120 can be arack of separate devices or a single device with multiple modems. Thus,the multiple transceiver devices of equipment 120 can be separatecircuit devices on a single integrated circuit (IC) chip, separate ICchips on a single circuit board, or separate electronic devices. In someimplementations, the multiple transceiver devices of the electronicequipment 120 can be installed in existing DSLAM equipment used toprovide DSL services. In some implementations, the multiple transceiverdevices of the electronic equipment 120 can replace existing DSLAMequipment used to provide DSL services.

In some implementations, the electronic equipment 120 can combine TimeDivision Multiplexing (TDM) with half duplex communication such that apair of communication devices do not transmit and receive at the sametime. By transmitting from electronic equipment 120 to the separatetransceiver devices 130 at the same time, and likewise receivingtransmissions at the electronic equipment 120 from the separatetransceiver devices 130 at the same time, NEXT interference can beavoided. This is true even while using the same frequency bands. Notethat while a specific common frequency band is not critical, thefrequency band used will typically be a common frequency band above thefrequency band used by an analog phone service of 0-4 kHz, and alsoseparated from this phone service frequency band by a guard band. Notethat the frequency band used can come from 2 MHz to 100 MHz and can beextended to 200 MHz for short distance cables. All the phone line pairsin the same telephone cable (i.e., the potentially interfering telephonelines) should use the same frequency band using the techniques describedherein to split time in downstream and upstream transmissions in asynchronized way.

In addition, each of the transceiver devices in the electronic equipment120 and the separate transceiver devices 130 can be G.hn transceiversdesigned for multipoint to multi-point communications over various typesof wiring, but repurposed here for single-point to single-point (or tomulti-point) communications over a telephone line. For example, thetransceiver devices in the electronic equipment 120 and the separatetransceiver devices 130 can be transceivers that are designed to operatein accordance with a G.hn specification. Thus, a DSL-like access networkcan be built with G.hn domains.

FIG. 2A shows an example of a transceiver device 200, which includes acoupling circuitry (Cpl) 205, an analog front end (AFE) 210, and acontroller (Cntrl) 215. The coupling circuitry 205 can be a coupler forphone line cables and phone line signals that is impedance matched tooptimize power transfer and minimize crosstalk. The coupling circuitry205 can include filter circuitry and/or be coupled with filtercircuitry, such as one or more high pass filters, and the AFE 210 caninclude biasing circuitry and a digital-to-analog converter (DAC) toconvert the analog signals to digital signals used by the controller215.

The controller 215 can be coupled with one or more network interface(Net Intrf) devices 230, such as a Gigabit Ethernet transceiver withmultiple ports and magnetics or a wireless (e.g., WiFi) access point(AP), or connected directly to a switch or packet processing unit. Inaddition, the controller 215 can be a baseband Digital Signal Processor(DSP) with embedded microprocessor(s) (h) 220 and associated memory 225,which can include non-volatile memory storing instructions (e.g.,firmware) that control operation of the DSP 215. In someimplementations, the controller 215 can include analog-to-digital (AD)and digital-to-analog (DA) converters. The transceiver device 200 isrepresentative of the devices on both the customer premises and thedevices located at the phone company's facility, which can coordinatetheir activity for signal to noise ratio estimation in the telephonelines of the shared cable as described below in connection with FIGS. 4and 5. In addition, in some implementations, these transceivers can havetheir communication over the telephone lines in the shared cablesynchronized as described further below in connection with FIGS. 2B, 2C,and 3.

FIG. 2B shows an example of transceiver devices 240 synchronized forcommunication on separate wires that share a common cable, such as abundled telephone cable (not shown). In this example, each transceiverdevice 240 operates as both a transmitter (Tx) and a receiver (Rx), andeach transceiver device 240 is a G.hn device that operates as a DomainMaster (DM), which coordinates transmissions over its respective domain(e.g, the telephone line connecting the transceiver device 240 to itscorresponding G.hn CPE transceiver (Tx/Rx) 260). The DMs have theirrespective Medium Access Control (MAC) cycles synchronized with eachother, and each DM splits its MAC cycle 250 into predefined time slots255 for downstream communication OWN) from the DMs to the CPEs andupstream communication (UP) from the CPEs to the DMs.

As shown in FIG. 2B, synchronizing the DMs causes their MAC cycles 250to be aligned for all communications across the telephone lines. In someimplementations, the synchronization can be readily done using existinghardware. An external MAC synchronization signal (e.g., a Zero Crossingsignal) input 242 for each transceiver device 240 (e.g., a zero crossdetector input to an IC chip) can be connected to a common referenceclock (Clk) 245 to synchronize the transceiver devices 240. This circuitis used in G.hn to synchronize all nodes in a G.hn domain with a commonpattern and is used here to synchronize all domains in one or moreDSLAMs. Thus, the same clock signal (e.g., a 50 Hz or 60 Hz clocksignal) can be connected to the signal input 242 of all DMs of thepotentially interfering G.hn networks to accomplish accurate timesynchronization. So rather than use an AC line of a power linecommunication (PLC) system to synchronize a MAC cycle, an externalsource is used to synchronize multiple MAC cycles for transceiversconnected to different wire pairs. Using the same clock can avoidpotential issues produced by clock deviations. The reference clockfrequency is flexible, and a clock frequency of 25 Hz or 50 Hz can beused to minimize potential customization needed in a G.hn system. Notethat this reference clock can be shared among all DSLAMs transmitting inthe same telephone cable and suffering from NEXT, and so the system isreadily scalable. In some implementations, the synchronization signalmay be derived from network packets based on IEEE (Institute ofElectrical and Electronics Engineers) 1588 Precision Time Protocol(PTP).

Thus, a DSL-like access network ca be built with G.hn domains. Onedomain with a pair of G.hn devices 240, 260 can be provided per line,with each domain for the respective telephone lines having a differentdomain identifier. Each DM 240 can be placed at a DSLAM at the telephonecompany's facility, and each respective CPE 260 can be placed at theseparate customer premises. Note that in some implementations, more thanone CPE 260 can be attached to the same phone line at a customer site.

By synchronizing in time all the DMs of the G.hn domains that couldinterfere (e.g., those present in the same DSLAM or injecting signal ina same multi pair telephone cable) and splitting the MAC cycle inprefixed slots for Downstream (DW) and Upstream (UP), the synchronouscharacteristic of the G.hn MAC can be leveraged to avoid NEXTinterference. The MAC can assign the time slots according to this rule,so each DM 240 can transmit only in DW slots, and each CPE 260 cantransmit only in UP slots. Thus, the transmission scheme is fixed andsynchronized in all G.hn domains so all downstream traffic (DM to CPE)occurs simultaneously, and likewise upstream (CPE to DM), preventingNEXT interference.

The clock reference defines the G.hn MAC cycle, and the MAC cycle isdivided into short time slots (e.g., sixteen time slots of 0.875 ms eachfor a MAC cycle of 14 ms) with each time slot being assigned to a fixedtransmission direction. This division allows the balancing in Downstreamand Upstream, but the same distribution must be configured in all DMhaving NEXT interference with each other. In the example shown in FIG.2B, the DW and UP time slots are evenly distributed in the synchronizedMAC cycles (50% in Up and 50% in Down). Thus, the predefined time slots255 alternate between DW and UP slots for the entire length of the MACcycle, which is sixteen slots in this example.

However, in other embodiments, the predefined time slots have anunbalanced distribution between downstream communication and upstreamcommunication. FIG. 2C shows an example of an unbalanced distributionbetween downstream communication and upstream communication forpredefined time slots in the communication system of FIG. 2B. In theexample shown, the unbalanced distribution favors downstreamcommunication (70% Down and 30% Up) since downloading at CPE sites willtypically be more common than uploading. The disfavored time slots (UPin this example) can be distributed in a manner that reduces latencythat might otherwise occur. The selection of the split between Down andUp is flexible (e.g., from 50/50 to 80/20) and can be defined and fixedprior to installation, which simplifies the system. In some casesthough, a dynamic and flexible distribution of Down/Up slots is possibleusing an external entity to inform in a synchronized way to alldifferent domains of the type (Down/Up) of each time slot.

Various approaches to distributing the disfavored time slots can beused. In the example shown, each MAC cycle includes sixteen time slots,and seven of each ten time slots are assigned for downstream (DW)communication, while three of each ten time slots are assigned forupstream (UP) communication, and the three UP time slots are distributedto reduce latency. Thus, each set of ten time slots 280, 282, 284, 286,288, 290, 292, 294 is divided into the following DW/UP pattern: DW, DW,UP, DW, DW, UP, DW, DW, UP, DW. Eighty is the first integer that isevenly divisible by both ten and sixteen, so the ten time slots 280,282, 284, 286, 288, 290, 292, 294 are distributed among five(eighty/sixteen) MAC cycles 270, 272, 274, 276, 278, as shown in FIG. 2C(note that the separate sections in FIG. 2C is showing a commonscheduling that rolls over and not different scheduling for differenttelephone lines in the same bundle). Other distributions are alsopossible. For example, a time slot pattern (such as DW, DW, UP) can berepeated across MAC cycles for a number of MAC cycles needed to form alarger repeating pattern (e.g., sixteen repetitions of the DW, DW, UPpattern across three MAC cycles of sixteen slots each).

While synchronizing the MAC cycles and aligning DW and UP time slotsacross multiple transceivers addresses NEXT interference, FEXTinterference can still be an issue. For example, in a G.hnimplementation, a receiver on one twisted wire pair could synchronizewith a transmitter on another twisted wire pair, thus reducingefficiency of the system. To address this issue, different orthogonalpreambles can be used in each transceiver controller (e.g., G.hn DM) totransform interfering signals into noise for other lines (e.g., theother G.hn domains). The orthogonal preambles can be similar to thosedefined in traditional G.hn, but more and different preambles than thestandard preambles specified for a home wiring phone line profile areprovided, as described herein.

Table 1 below shows three hundred different seeds used to generate thepseudo-random sequences of the preambles for a phone profile inaccordance with the systems and techniques described herein. The seedsare shown in hexadecimal format and have been designed to provide goodinsulation between the different preambles generated; note that not allpreambles have the same characteristics. Moreover, the provision ofthree hundred different preambles can facilitate the use of equipmentwith bundled telephone cables with different numbers of twisted wirepairs, as enough preambles will be available regardless of whether thebundled telephone cable has ten, twenty, twenty five, fifty, seventyfive, one hundred, one hundred and fifty, or three hundred wire pairs.

TABLE 1 Seeds for Orthogonal Preambles for Telephone Profile 0x024E0x1C1D 0x1358 0x0583 0x15BC 0x0042 0x01F0 0x0BB9 0x1D50 0x1AB3 0x17A90x1ADE 0x12D7 0x08E9 0x0D3A 0x0432 0x07A4 0x1CA3 0x1D26 0x1C70 0x0F530x1B5B 0x1016 0x054A 0x0B06 0x0340 0x041D 0x13F8 0x121A 0x0686 0x10F30x05B3 0x02DE 0x0397 0x11D2 0x1992 0x0AE0 0x0021 0x1B4E 0x16B8 0x15450x084F 0x0B14 0x016F 0x0A95 0x0819 0x1491 0x0219 0x03E1 0x01D0 0x01E60x0029 0x1437 0x058A 0x072F 0x1EA3 0x185D 0x11A0 0x0F48 0x1E55 0x0A8A0x0637 0x0AF6 0x0A1B 0x03F9 0x0EA5 0x0BF0 0x1CC9 0x083B 0x0294 0x098E0x121E 0x15CF 0x157B 0x1C49 0x1FC4 0x08A7 0x0BB6 0x15C0 0x155A 0x06B20x1EFB 0x1E04 0x1AE7 0x1F75 0x1A86 0x1671 0x1033 0x0923 0x07A0 0x17C90x102F 0x0CDF 0x0F02 0x1EC4 0x0AA1 0x1E92 0x1D46 0x10BA 0x1867 0x00A70x154F 0x14AF 0x066F 0x1428 0x19D9 0x1E24 0x1D4B 0x17E0 0x18BB 0x131C0x14C7 0x1530 0x0A57 0x0553 0x0D3B 0x0FBA 0x1F88 0x114E 0x0B47 0x0D640x0CDE 0x1B55 0x0A98 0x0596 0x01D5 0x0F62 0x150D 0x0CE2 0x0297 0x0F930x0880 0x085F 0x0DAA 0x00BB 0x191B 0x1A14 0x1542 0x1D24 0x1E10 0x014F0x09AC 0x0592 0x042F 0x135D 0x1DCA 0x02A9 0x13B3 0x176C 0x0EDA 0x14FC0x096B 0x1B2A 0x12C9 0x0A5D 0x0C62 0x12CB 0x1A76 0x0D18 0X04B4 0x044C0x0D6F 0x1E42 0x1D95 0x1539 0x09E7 0x105D 0x03AB 0x1A0C 0x0E9D 0x0B960x0DAD 0x07E8 0x01FC 0x1E4C 0x12BE 0x19AE 0x1236 0x0D9F 0x0576 0x040D0x02D9 0x1503 0x1C85 0x19A7 0x161B 0x052E 0x1B94 0x097D 0x1120 0x01190x0427 0x0F10 0x0FD0 0x1B4B 0x06DC 0x1A9C 0x18C4 0x0C80 0x1B29 0x037E0x1014 0x038A 0x0A06 0x186E 0x0E36 0x0F26 0x13CE 0x03FA 0x080A 0x00740x131B 0x0A34 0x1E20 0x1522 0x10E5 0x0CD3 0x057C 0x1C26 0x196C 0x1A7E0x180B 0x1878 0x0715 0x1CE2 0x0389 0x0DA5 0x0C36 0x0DE6 0x0541 0x02260x043D 0x1170 0x1469 0x1EB0 0x1955 0x0C37 0x0DB8 0x1CB4 0x15DF 0x1E0E0x1DF6 0x03E4 0x10F0 0x1547 0x1C12 0x0A91 0x1C6C 0x0F2C 0x195D 0x172C0x005F 0x1251 0x02E1 0x083C 0x17BA 0x0E71 0x01CA 0x14BC 0x172B 0x081B0x0A9E 0x0253 0x07C9 0x001C 0x1EA8 0x0F58 0x0713 0x1FAE 0x055E 0x02320x098F 0x0F66 0x04A3 0x1772 0x1E93 0x1AA3 0x12AA 0x1971 0x1FDA 0x06FC0x19BD 0x0ADE 0x04A6 0x1946 0x190D 0x141E 0x1825 0x02C8 0x0755 0x00E80x1100 0x069D 0x1ECC 0x07F0 0x1DA7 0x000E 0x0F75 0x0584 0x03A7

FIG. 3 shows an example of a process for communicating on a phone lineof a bundled telephone cable having multiple phone lines. At 300, anorthogonal preamble is selected from a set of available preambles foruse on a telephone line that is grouped with additional telephone linesin a bundled telephone cable. In some implementations, three hundreddifferent preambles can be made available. Moreover, the selection canbe based on line number. For example, there can be a fixed relationshipbetween a line's ordinal number in the bundled telephone cable thepreamble selected for the line. This can simplify device installation.

At 310, the MAC cycle is synchronized with MAC cycles of additionaltransceiver devices connected respectively to the additional telephonelines grouped in the bundled telephone cable. For example, each of theMAC cycles can be synchronized to a common clock reference signalprovided on a signal input (a Zero Crossing signal input) in (G.hnimplementations. At 320, the MAC cycle is split into predefined timeslots aligned across communications on the additional telephone lines bythe additional transceiver devices. The predefined time slots includetime slots for downstream communication and time slots for upstreamcommunication and can be short relative to the MAC cycle (e.g., the MACcycle can be divided into sixteen slots).

At 330, a determination can be made regarding whether to have a balanceddistribution of downstream and upstream slots, or an unbalanceddistribution. For example, at the time of installation (or upon a resetoperation) an input can be provided that indicates the type of slotdistribution to use, and this input can be processed to determine thetype of distribution to effect. If a balanced distribution is to beused, this is done so at 360. If an unbalanced distribution is to beused, this can be a predefined unbalanced distribution, or a process canbe employed to define the unbalanced distribution based on variousfactors, including potentially user input.

At 340, more time slots can be assigned to downstream communication thanupstream communication. In some implementations, the reverse can bedone, but in typical implementations there will be more downstreamcommunications than upstream communications. For example, the assigningcan involve assigning seven of each ten slots to downstreamcommunication and three of each ten slots to upstream communication.Other ratios are also possible. In addition, at 350, the time slotsassigned to upstream communication (or downstream in the case thatdownstream communication is given fewer slots) can be distributed toreduce latency. This can involve distributing the slots across multipleMAC cycles, such as described above.

At 370, communication signals are sent on the telephone line in thedownstream time slots using the selected orthogonal preamble. Note thatthe preamble is the first signal sent on the line and can be used tosynchronize the transmitter with the receiver. At 380, communicationsignals are received on the telephone line in the upstream time slots.As will be appreciated, the sending and receiving are an ongoingprocess, even though shown in the figure as sequential operations.

Furthermore, before full speed communication of data signals cancommence on a telephone line, an estimation of signal to noise ratio(SNR) on that telephone line is typically needed. Although NEXT (NearEnd Crosstalk) can be reduced by synchronizing the upstream anddownstream transmissions, and FEXT (Far End Crosstalk) can also be atleast Martially addressed using orthogonal preambles, as describedabove, there can still be an issue related to FEXT, producing a variableSNR depending on whether there are concurrent transmissions in theadjacent lines.

This instability in the SNR can produce a problem in the receivers whendoing channel adaptation, which determines the number of bits persub-carrier to use or bit allocation table (BAT). The root cause of theproblem is that the amount of interfering signal may be different whenmeasuring the channel SNR and deriving the BAT than when using thatestimated BAT during data transmission. If the SNR during datatransmissions is lower than the SNR during BAT estimation, the BLER(block error rate) may be too high.

FIG. 4 shows an example of a process for increasing stability of SNRestimation on a phone line of a bundled telephone cable having multiplephone lines. At 400, an indication is received at a first transceiverdevice coupled with a first telephone e. The indication identifies thata second transceiver device coupled with a second telephone line is toestimate SNR on the second telephone line, where the second telephoneline is separate from but grouped with the first telephone line withrespect to possible FEXT.

SNR estimation can be done at start up and periodically or by means of atrigger (change in BLER, for instance). A DSLAM can have a CentralProcessing Unit (CPU) for managing the equipment. This CPU has amanagement interface with all the DMs. If a DM needs to estimate SNR (orits attached CPE), the DM can use the management interface with that CPUto signal this, and the CPU can broadcast the request to the rest of DMsusing the management interface. This interface can be implemented by aprotocol over an Ethernet link. In addition, the MAC cyclesynchronization allows having a common time base to signal when the SNRestimation period starts and ends.

At 410, a check is made in response to the indication as to whether datais to be transmitted by the first transceiver device on the firsttelephone line during the SNR estimation by the second transceiverdevice on the second telephone line. Data packets are stored in queueswaiting for the time slot in the MAC to be able to be transmitted.Therefore, if the slot arrives and the queue is empty, there is not datato transmit. Queues can be monitored before each transmissionopportunity. In a time slot, several transmissions, called frames, canbe sent. Those transmissions are separated by a small idle time calledIFG (interframe gap). In the case where there is only data for only apart of the SNR estimation time, the rest of the time is completed bytransmitting PROBE frames (SNR estimation frames loaded with data fromthe LFSR or PR sequence). Thus, data frames can be followed by PROBEframes during that SNR estimation time. Note that the IFG idle time isnot affecting the SNR estimation because the IFG idle time is very shortin duration.

If data is available for transmission at 420, then a data signal istransmitted at 430 on the first telephone line during the SNR estimationby the second transceiver device on the second telephone line. On theother hand, if data is not available for transmission at 420, then analternative signal is transmitted at 440 on the first telephone lineduring the SNR estimation by the second transceiver device on the secondtelephone line. It should be noted that this runs counter to thetraditional G.hn specification, in which anode remains silent when thenode does not have data to transmit. In addition, although the exemplaryprocess described in connection with FIG. 4 involves a signalingprotocol that forces transmission of the alternate signal only whenanother transceiver device is going to estimate the SNR, someimplementations the forced transmission of an alternate signal can occurwhenever the transceiver device has no data to transmit. In contrast,the signaling protocol described in connection with FIG. 4 allows thenodes to remain muted if there is no data to send once the channel hasbeen estimated, as the worst case had been measured, thus saving power.

Various options are available for transmission of the alternative signalat 440. In some implementations, transmitting the alternative signalinvolves generating an uncorrelated pseudo-random (PR) sequence, at 442,and modulating sub-carriers of the transmission (e.g., the payload of aprobe frame) with the generated PR sequence at 444. The PR sequence (andthus the transmission) can be made uncorrelated with other PR sequences(and thus other transmissions) on the other telephone lines in atelephone cable by using different pseudo-random function generators orby using different initial seeds to the same pseudo-random functiongenerator. In some implementations, the same pseudo-random functiongenerator can be used in all transceiver devices coupled with telephonelines in a group, and the initial seed can be different for each pair oftransceiver devices (DM and one or more CPEs) coupled to the sametelephone line, or each transceiver device can have its own, uniqueinitial seed. Such seeds can be chosen so as to generate uncorrelated PRsequences with the peak to average ratio (PAR) of the generatedOrthogonal Frequency Division Multiplexing (OFDM) symbols being below athreshold Co avoid clippings. In some implementations, the seeds ofTable 1 above can be used. The DM can be assigned a seed value, and theDM can communicate that seed value to its CPEs.

FIG. 5 shows an example of a communication system 500 with differentconcurrent operations of transceiver devices coupled with separate wiresthat share a common cable. Each of the wires in the figure is shown asbeing a twisted copper pair, but other types of telephone lines, as wellas other wire configurations (e.g. a power line or coax cable) are alsopossible. The system 500 shows only the transceiver devices on one sideof the telephone lines, but the description below applies equally toboth sides, so the side shown can be either the DM side or the CPE side.In addition, even though significant portions of this description aremade with reference to the G.hn specification, other implementations arepossible, as will be appreciated.

The system 500 shows four transceiver devices, but fewer or moretransceiver devices are also possible. Some implementations will includeseventy five, one hundred, one hundred and fifty, or three hundredtransceiver devices on each side of the telephone lines, and potentiallymore on the CPE side since each customer location can have more than onetransceiver device coupled with the same telephone line. In addition,FIG. 5 shows a particular point in time when one of the transceiverdevices is estimating SNR, two of the transceiver devices aretransmitting an uncorrelated PR signal, and one of the transceiverdevices is transmitting an encoded data signal, but it will beappreciated that each of the transceiver devices can take on each ofthese different operations at different times. The key point is that agiven transceiver device (or node in the system 500) is forced totransmit (always or selectively) even when that transceiver device hasno data to transmit, in order to avoid instability in SNR estimation.

A first transceiver device 510 generates and transmits an SNR estimationsignal 512. This can involve channel estimation and adaptation. In someimplementations, the number of bits per sub-carrier to use isdetermined, and a bit allocation table (BAT) is constructed. In someimplementations, this is done in accordance with the G.hn specification.In some implementations, a channel estimation probe frame is transmittedwhere the probe symbols composing the payload are all channel estimationprobe symbols. These channel estimation probe symbols can be generatedby a linear feedback shift register (LFSR) 514 whose initial seed 516for the first sub-carrier of the first symbol of the payload is adefault value (which can be fixed in accordance with a G.hnspecification) that is known at the receiving side. Thus, the knownsequence can be used at the receiving side to estimate the signal tonoise ratio on the channel.

Concurrent with the transmission of the SNR estimation signal 512, asecond transceiver device 520 and a third transceiver device 530, whichare both connected with separate telephone lines that are grouped withthe first telephone line for the first transceiver device 510, transmitrespective uncorrelated PR signals 522 and 532. These signals 522 and532 are forced transmissions that would normally not occur because thetransceiver devices 520 and 510 have no data to transmit at that time.But by forcing transmission on these other telephone lines concurrentwith the SNR estimation by the first transceiver device 510, thereceiver(s) on the other side of the telephone line from the transceiverdevice 510 can get a more accurate assessment of the SNR likely to beseen during normal operation.

Note that a fourth transceiver device 540, which is also designed Coprovide forced transmissions, does not have a forced transmission at thesame time since the fourth transceiver device 540 has an encoded datasignal 542 to send on its telephone line. Further, as noted above, theforced transmissions can be done whenever there is no data to send(i.e., always do forced transmissions) or whenever there is both no datato send and one or more other transceiver devices are estimating SNR. Ineither case, providing a system in which such forced transmissions aremade allows the receivers in the system to estimate a more stable SNR asthe interference is stable, thus potentially diminishing errors, latencyand jitter. In a sense, the system can be viewed as working in a morestable “worst case” scenario.

In some implementations, the forced transmissions 522 and 532 can beprobe frames, such as those used in G.hn for channel estimation. Thus,when a device has a time slot assigned for transmission and the devicehas no data to transmit, the device can program a probe frametransmission so that the adjacent links suffer a stable interference. Inthe probe frames from respective devices 520 and 530, sub-carriers canbe loaded with bits coming from respective LFSRs 524 and 534. But it maynot be desirable to have different nodes generate probe frames with thesame bit sequence modulated in the sub-carriers of the same payloadsymbols, which can have a negative side effect in a DSL-like phoneaccess application because several nodes might be transmittingsynchronized probe frames with the same contents. In this case, theinterference coming from other lines (domains) might add coherentlyproducing a higher (or lower if the interference is destructive) levelof interference compared with the case of uncorrelated transmissions(normal case when transmitting data when signals add-up no coherently)preventing a good accurate SNR estimation.

To address this issue, the respective LFSRs 524 and 534 can usedifferent initial seed values for their pseudo-random sequencegeneration: alternative initial seed A 526 and alternative initial seedB 536. Note that although device 540 is shown in FIG. 5 as having anencoder 544 generating the encoded data signal 542 from inputinformation 546, the device 540 also has an LFSR and its own differentseed value for use when the device 540 does not have data to send whileanother device is doing SNR estimation. Likewise, the device 510 has itsown different seed value for use when the device 510 does not have datato send while another device is doing SNR estimation, and each ofdevices 510, 520 and 530 have encoders for data transmission for usewhen the devices 510, 520 and 530 have information to send on theirrespective telephone lines.

In some implementations, a different initial seed can be provided perdomain (pair of nodes in one line). Each respective LFSR can generate agiven fixed pseudo-random sequence where the initial seed determines theoffset in that sequence to make the bits required to modulate the firstsub-carrier of the first payload symbol. In some implementations, thespecific offset into the sequence is not important, provided the offsetsused by different transceivers on the different telephone lines aredifferent, since the generated symbols are intended to be simply randomand therefor lack information content. By choosing different initialoffsets into the generated sequence (different initial seeds) perdomain, the probe frames generated by other domains will be different.This prevents probe frames from different domains from adding upcoherently.

A few embodiments have been described in detail above, and variousmodifications are possible. The disclosed subject matter, including thefunctional operations described in this specification, can beimplemented in electronic circuitry, computer hardware, firmware,software, or in combinations of them, such as the structural meansdisclosed in this specification and structural equivalents thereof,including potentially program operable to cause one or more dataprocessing apparatus to perform the operations described (such as aprogram encoded in a computer-readable medium, which can be a memorydevice, a storage device, a machine-readable storage substrate, or otherphysical, machine-readable medium, or a combination of one or more ofthem).

The term “data processing apparatus” encompasses all apparatus, devices,and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

While this disclosure contains many specifics, these should not beconstrued as limitations on the scope of what may be claimed, but ratheras descriptions of features that may be specific to particularembodiments. For example, details are provided with regard to G.hnimplementations. However, the systems and techniques described hereincan also be employed in systems using Time Division Multiple Access(TDMA), like the IEEE (Institute of Electrical and ElectronicsEngineers) Standard 1901 or ITU G.Fast.

Certain features that are described in this specification in the contextof separate embodiments can also be implemented in combination in asingle embodiment. Conversely, various features that are described inthe context of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments.

Other embodiments fall within the scope of the following claims.

What is claimed is:
 1. A system comprising: telephone lines that cover adistance from a first location to separate points at second locations,wherein the telephone lines are bundled together in a same telephonecable for at least a portion of the distance; electronic equipmentlocated at the first location, the electronic equipment comprising afirst transceiver device for each of the telephone lines, wherein eachfirst transceiver device at the first location is configured tocoordinate transmissions over a respective telephone line coupled withthe first transceiver device; and second transceiver devices coupledrespectively with the telephone lines at the second locations, such thateach second transceiver device is respectively paired with a firsttransceiver device at the first location; wherein each pair of first andsecond transceiver devices is configured to communicate over therespective telephone line connecting the pair using a Medium AccessControl (MAC) cycle that is split into predefined slots in time for (i)downstream communication from the first transceiver device to the secondtransceiver device and (ii) upstream communication from the secondtransceiver device to the first transceiver device; and wherein thefirst transceiver devices are synchronized with each other to align theMAC cycle and the predefined time slots across the telephone lines. 2.The system of claim 1, wherein each transceiver device at the firstlocation is configured to operate in accordance with a specificationdesigned for multi-point to multi-point communications over homeelectrical wiring, at least one of the second locations has more thanone second transceiver device coupled with a single telephone line, andthe more than one second transceiver device share the upstreamcommunication slots on the single telephone line.
 3. The system of claim2, wherein the specification is a G.hn specification.
 4. The system ofclaim 3, wherein a Zero Cross signal input of each of the firsttransceiver devices is connected to a common reference clock tosynchronize the first transceiver devices.
 5. The system of claim 1,wherein the predefined slots in time have an unbalanced distributionbetween downstream communication and upstream communication.
 6. Thesystem of claim 5, wherein the unbalanced distribution assigns more timeslots to downstream communication than upstream communication, and timeslots assigned to upstream communication are distributed to reducelatency.
 7. The system of claim 6, wherein the unbalanced distributionassigns seven of each ten slots to downstream communication and three ofeach ten slots to upstream communication.
 8. The system of claim 1,wherein each one of the first transceiver devices is configured to use apreamble that is different from each other preamble used by remainingones of the first transceiver devices.
 9. The system of claim 8, whereinthe first transceiver devices are configured to use up to three hundreddifferent preambles.
 10. A transceiver device comprising: a couplingcircuitry configured to connect with a telephone line that is bundledwith additional telephone lines in a telephone cable; an analog frontend coupled with the coupling circuitry; and a controller coupled withthe analog front end and configured to coordinate transmissions over thetelephone line; wherein the controller is configured to split a MediumAccess Control (MAC) cycle for the transmission into predefined slots intime for (i) downstream communication to another transceiver devicecoupled with the telephone line and (ii) upstream communication from theother transceiver device; and wherein the controller is configured tosynchronize the MAC cycle with MAC cycles of additional transceiverdevices coupled with the additional telephone lines in the telephonecable to align all the MAC cycles and the predefined time slots acrossthe telephone lines.
 11. The transceiver device of claim 10, wherein thecoupling circuitry, the analog front end, and the controller areconfigured to operate in accordance with a specification designed formulti-point to multi-point communications over home electrical wiring.12. The transceiver device of claim 11, wherein the specification is aG.hn specification.
 13. The transceiver device of claim 12, comprising aZero Cross signal input connected to a common reference clock tosynchronize all the MAC cycles and the predefined time slots across thetelephone lines.
 14. The transceiver device of claim 10, wherein thecontroller comprises a baseband digital signal processor programmed touse an unbalanced distribution for the predefined time slots betweendownstream communication and upstream communication.
 15. The transceiverdevice of claim 14, wherein the baseband digital signal processor isprogrammed to assign more time slots to downstream communication thanupstream communication and to distribute time slots assigned to upstreamcommunication to reduce latency.
 16. The transceiver device of claim 15,wherein the baseband digital signal processor is programmed to assignseven of each ten slots to downstream communication and three of eachten slots to upstream communication.
 17. The transceiver device of claim10, wherein the controller is configured to use a preamble that isdifferent from each of other preambles used by the additionaltransceiver devices.
 18. The transceiver device of claim 17, wherein thecontroller is configured to select the preamble from a set of threehundred different available preambles.